The scale on a map is 9cm : 7km. If two cities are 72cm apart on the map, what is the actual distance in km between the two cities?
Explanation: The scale means that every 9cm on the map corresponds to an actual distance of 7km. A distance of 72cm on the map is the same as 8 $\cdot$ 9cm. The actual distance between the two cities is 8 $\cdot$ 7km, or 56km.